In a double-thread twister a pair of yarn packages are normally stacked on a twister spindle and a thread, yarn or filament is pulled off from each of these packages, up around the two yarn packages, and passed down through the hollow spindle. There is normally provided in this spindle a so-called thread brake which pinches the two yarns and tensions them to the extent necessary for proper twisting (see German Offenlegungsschrift DT-OS No. 23 09578).
Such a thread brake normally has a housing with a vertically elongated relatively narrow passage. The housing is formed along this passage with a relatively wide compartment in which is provided a braking element. This element may be a spring-loaded capsule, a ball, or any other similar arrangement which presses a thread or threads passing along the passage against a wall of the compartment so as to tension them as described above.
In order to thread such an arrangement, that is in order to pass the filaments being twisted down through the thread brake, it is necessary to displace the braking element into a position clear of the thread passage. This can be done by providing external means, such as an electromagnet or a permanent magnet which pulls the braking element to the side. It is then possible to pass the filament or filaments down through the thread brake. This threading operation is normally carried out by means of a pneumatic threader which is fitted to the top of the twisting spindle and blows the filaments down through the thread passage once the braking elements has been displaced out of the way.
Such an arrangement has the considerable disadvantage that the relatively wide compartment midway down that thread passage often creates turbulence in the pulse of air that carries the filaments along this thread passage so that the filaments become caught in this compartment. Thus as these filaments are carried downwardly along the thread passage the stream of air carrying them slows suddenly in the braking compartment and the filaments can then catch on the braking mechanism therein. For this reason it is frequently necessary to make several attempts to shoot the filaments down along the thread passage, as rarely can the filament be displaced past the braking compartment on the first try. Such a disadvantage therefore slows the twisting operation and has a correspondingly poor effect on plant efficiency.